Promontorio di Ansedonia, Coastal promontory in Tuscany, Italy.

Promontorio di Ansedonia is a headland at the southern end of the province of Grosseto, in the municipality of Orbetello. Its summit, 113 metres above sea level, coincides with the acropolis of the Roman city of Cosa. It closes the Feniglia tombolo to the east and borders the ferruginous beaches to the west, with the Torre di San Pancrazio and Torre di San Biagio on its seaward slopes.

The area was an important Roman settlement in antiquity, with the City of Cosa dating from the 3rd century BC. Medieval watchtowers were built later to defend against pirate raids and protect the coast.

The name Spacco della Regina marks the deep cleft cut into the eastern shore, where the Tagliata Etrusca channel and the Spacco itself were carved to keep the ancient Etruscan-Roman harbour clear of sand. Visitors can still walk the rock-cut channel and see the towers of San Pancrazio and San Biagio on the seaward slopes.

The summit at 113 metres coincides with the Acropolis of Cosa, reached on foot along trails; the coastal towers of San Pancrazio to the west and San Biagio to the east stand on the sea-facing slopes. The southern shore is high and rocky, so bathing is on the Feniglia tombolo and the ferruginous beaches rather than below the cliffs.

The Spacco della Regina is not a cave but a narrow artificial channel cut into the rock near the eastern shore, part of the hydraulic works protecting the ancient Etruscan-Roman harbour. Together with the nearby Tagliata Etrusca it is easy to walk past without noticing.